1. Field of the Invention
The present invention relates to an amplifier, and more specifically to a high-power amplifier.
2. Description of the Related Art
In recent years, a demand for a wireless communication system capable of transmitting/receiving large-capacity data at a high speed grows along with widespread use of the Internet. A higher power is required of a high-power amplifier as one of the components of the system, in particular, a power amplifier used in a wireless communication base station.
If an amplifier is configured by a large transistor (high-power transistor) for that purpose, an output impedance of the transistor is lowered. Thus, the impedance needs to be converted for load matching (impedance matching).
A conventional microwave high-power amplifier includes, for example, an input matching circuit 100, a high-power transistor 101, and an impedance converter circuit 102 as shown in FIG. 8. In FIG. 8, reference numeral 104 denotes a bias transmission line; 105, a terminal resistor; and Z1, Z2, Z3, and ZL, an impedance value.
The impedance converter circuit 102 includes, for example, a ¼-wavelength transmission line 103 as shown in FIG. 8. Therefore, a line length is increased. In particular, the line length is very long in a low microwave frequency band.
In general, an output impedance of the high-power transistor 101 is as low as about several Ω, for example. Thus, as for an application that requires a wide band, it is necessary to provide three ¼-wavelength transmission lines 103 and execute impedance conversion in three steps as shown in FIG. 8, for example.
As described above, the microwave high-power amplifier has a problem of increasing footprint. In particular, a large space is necessary when a large bandwidth is required.
Further, a hybrid integrated amplifier that combines various components has been hitherto used as a microwave high-power amplifier. This amplifier has a problem about a high mounting cost.